Patent GB-1253431-A (GB)
Title: Method and apparatus for optically recording colour picture information on a photographic medium
IPC: H04N5/84
Filed: 1969-03-26
Abstract: 1,253,431. Colour television. COLUMBIA BROADCASTING SYSTEM Inc. 26 March, 1969 [1 April, 1968], No. 15821/69. Heading H4F. [Also in Division G2]  Chrominance information from an original scene is recorded by a camera on a monochrome photographic medium in a coded format suitable for scanning to develop video colour television signals by analysing an image of the scene into a series of parallel bands, each band including at least two identical strips which are subdivided into adjacent portions to provide displaced images of different colour components of the corresponding band area of the scene, and exposing the photographic medium to the series of bands and to a parallel optical image of a further series of alternating, relatively contrasting, bands of constant periodicity differing from the periodicity of the image strips to provide a reference series of positions. In a first embodiment of camera, light passing through a lens 25 either passes through, or is reflected by, two sets of red, blue and green dichroic mirrors 38-40 of a filter 26 the transmitted light being brought to a focus at 18 on one half of a film 10. The widths of the dichroic mirrors being equal, the transmitted light is recombined in the focused image to give a luminance image. The reflected light passes into a prism 31, is reflected at 32 towards a surface 34 of the prism which forms a series of cylindrical lenses 35 serving to divide the image into bands formed of adjacent portions 46, 48, 50 corresponding to the reflections from different dichrpics, i.e. two strips of three portions, which are recorded on the other half of the film at 20. Fig. 6 shows the images recorded from a scene consisting of parallel red, blue and green bands. An opaque mask 42 with light diffusing reflective areas 44, e.g. white paint or aluminized ground glass is located in the plane of the filter 26 and thus directs an average scene illumination towards the prism face 34 where the light is focused on to the film 10 to form the further series of reference bands 52. The length of the area 44 is half that of the filter 26 so that bands 52 are spaced apart by a distance equal to their width. The prism 31 serves to ensure that the images formed at 18 and 20 are both in focus despite the different path lengths, although additional lenses may also be used. The combination of film response and filter transmissivity should be chosen to approximate the luminance and chrominance characteristics used in the colour television system and the halves of the film may have different speed ratings of spectral responses to compensate for differences in light transmission in the different optical paths. Fig. 8 (not shown) shows an arrangement in which the dichroic mirrors 38- 40 are arranged in overlapping relationship to give an angular spacing of different colour components compatible with the colour phases of an NTSC colour signal. In a second embodiment, Fig. 9 (not shown), the filter 26 is immediately below and parallel with the lens 25. The reference series of lines 52 is provided by a light source operated in synchronism with the exposure of the film 10 and shining on to the prism face 32 through a mask, e.g. of ground glass. A third embodiment, Fig. 10 (not shown), has separate compartments and lenses for forming the chrominance and luminance pictures. A flexible light transmissive tube transmits light to the film when the camera shutter is open to provide a signal to maintain the film motion and vertical scanning rate in synchronism during reproduction. In a further modification the film itself is lenticulated and includes a series of colour filters below each lenticule, the lens 34 and filter 26 being omitted. A latent image of the reference series of lines 52 can be prerecorded on the film. The camera may be of the still or motion picture type.